Accidents often are caused by motor-powered machinery or implements such as lawnmowers, snowblowers, etc. In an effort to alleviate the dangers associated with operating such implements, manufacturers often have equipped them with deadman switches which automatically shut the engine off and/or brake a rotary driven element to a stop should the operator, for instance, let go of the handle. The deadman switch assures that if the operator trips and falls, or leaves the implement unattended, the engine immediately stops, reducing the danger of injury. Although noble in theory, such deadman switches can become impractical in operation because each time the operator must let go of the handle, e.g., to pick up debris from a lawn, the engine must be restarted. This often leads to consumer frustration and, occasionally, to attempts to circumvent the safety device.
To alleviate this drawback, some manufacturers have utilized a clutch-brake assembly which allows the functional or rotary part of the implement, e.g.; a lawnmower blade, to be disengaged from the engine by means of a clutch before such part is braked to a stop. With this design, the engine continues to run while the implement is unattended, but the dangerous part is incapacitated by the clutch-brake mechanism.
Such clutch-brake assemblies provide safety without undue inconvenience to the operator, but present new problems. Most clutch-brake assemblies are expensive to manufacture for a number of reasons Such assemblies commonly are manufactured to very close tolerances. Frequently the assembly must be sealed to prevent fouling from grass clippings or other foreign matter, particularly when such exacting tolerances are involved. Because of design limitations, such assemblies usually include a great many parts which often must be laboriously assembled part-by-part onto the implement housing.
Motorized implements which might utilize a clutch-brake assembly generally also incorporate flywheels. Most flywheels, however, are either expensive to manufacture or are unduly heavy. For example, flywheels can be manufactured relatively cheaply by simply forming a round metal disc in a stamping operation and then welding several of the discs together to form a heavy flywheel. A significant portion of the mass of such flywheels is carried near the central axis where little angular momentum is generated, thus causing the flywheel to be unduly weighty in relation to the angular momentum attainable. To reduce weight, flywheels have been machined from discs to remove much of the flywheel thickness near the central portion while leaving a greater mass at the periphery. Such a configuration maximizes the effectiveness of the flywheel while minimizing its total weight. Unfortunately, this manufacturing process is also rather expensive.